You can prevent Blender from crashing itself and probably thereby X by rendering in parts - check those renderbuttons named X-parts and Y-parts: change to an appropriately high value to make Blender render your image in a bunch of segments rather than the whole thing at once. That will decrease the amount of allocated memory for each pass, and you will probably not have a crash.

For example: X-parts: 3 Y-parts: 3 = Your image will render in 9 smaller parts, which will be stitched together once they are all completed.

This works very good for me (I've only got 256 MB ram, but I've rendered huge images without crashes [close to 1 meg polys at 4K resolution]).